The long-term goal of this project is to develop a new technology to improve the diagnosis of breast cancer. To accomplish this, we will combine the complementary aspects of real time Ultrasound (US) and Electrical Impedance Tomography (EIT) to form in-register enhanced images from a single bimodal probe. Electrode arrays will be added to a conventional ultrasound transducer array, and the ultrasound and EIT images will be displayed together, initially side-by-side, but ultimately by image fusion visualization software. EIT makes images of the interior of the body from measurements made at its surface. Small electric currents are passed through the body using electrodes applied to the skin; the resulting voltages are then measured and used to reconstruct the values of the electrical conductivity and permittivity of the underlying structures. The electrical properties of breast tumor tissue differ by a factor of 5 -10 from those of surrounding, normal tissue. By forming images of the electrical conductivity and permittivity of the breast using several different frequencies of electrical current, the technique is called tissue spectroscopy, and further diagnostic information may be elucidated. Ultrasound can be used to resolve ambiguous findings from x-ray exams, to discriminate between fluid cysts and solid lesions, to identify palpable abnormalities, and to guide interventional procedures such as needle biopsy. Weaknesses of ultrasound include lack of adequate spatial resolution and its inability to image well in dense and deeper tissue. The first year goal is to demonstrate proof of the combined modality concept. Images from both modalities will be recorded simultaneously and reconstructed off-line. Tissue-mimicking phantoms with appropriate acoustic and electrical properties for breast lesions will be visualized in a 2-D ultrasound image plane in register with a 2-0 slice from a 3-D EIT image. Each modality will be used to image things invisible to the other. The feasibility of using a combined-mode probe in normal human subjects will be demonstrated. In later years, a real-time combined 3-D EIT and 3-D ultrasound imaging system will be produced and evaluated for its ability to improve the sensitivity and specificity of breast cancer diagnosis. A dual US-EIT system could become an alternative to mammography in some patients, which might increase patient compliance with regular screening recommendations. This would reduce morbidity and mortality. [unreadable] [unreadable] [unreadable]